The preparation of 1,2-diols with a larger number of carbon atoms is a technically not yet satisfactorily solved problem. The preparation by hydrolysis of the corresponding 1,2-epoxide compound has been recommended repeatedly, but no solution satisfactory in all respects has yet been found. Disadvantages of the processes known so far are particularly the high consumption of chemicals and/or the high temperatures and the high pressures associated with this, which are required for the production of satisfactory yields.
For example, a process starting with the corresponding olefins and proceeding via the formation of epoxides is suggested by Swern et al in J. Am. Chem. Soc. 68: 1504-1507, 1946. Here, a large excess of formic acid is required as solvent and oxygen transfer agent (performic acid). The consumption of chemicals is increased, in addition, by the fact that the diol esters formed first are saponified with alcoholic potassium hydroxide solution.
The process of Merk et al, German published application De-OS No. 22 03 806, which utilizes a 2% sodium hydroxide solution for the epoxide hydrolysis, requires a smaller amount of chemicals. Here the disadvantages are the high reaction temperature (250.degree. C.) and the high pressure (about 40 atm.) which make complex pressure equipment necessary. The exchange of the sodium hydroxide solution for di- and monocarboxylic acid salts improves the diol yields, but requires the same high reaction temperatures.
The suggestion is made by Osberghaus et al U.S. Pat. No. 3,933,923, to achieve a greater yield by the use of acetone as solubilizer and disodium azelate as hydrolyzing agent. The work must be carried out at high temperature (250.degree. C.) and corresponding pressures, even in this case. It is also known that acid hydrolysis with dilute sulfuric acid produces considerable quantities of epoxide polymers in addition to about 50% diol.
For the hydrolysis of short-chain epoxides (ethylene oxide and propylene oxide), Cipriani et al, German Published Application DE-OS No. 26 15 595, recommend working in the presence of tertiary amines (triethylamine) and carbon dioxide at 110.degree. C. and 19 bar, with a hydrolysis time of 2 hours. The short-chain glycol forms with high selectivity. The application of this reaction to epoxide compounds with a larger number of carbons has failed so far.